Buffer pending results on session close

[ali-ince]

When a session is closed before consuming results of executed statements, we previously did not handle pending results and directly close the underlying connection - which contradicts with behaviour from other official drivers.

A sample code snippet demonstrating the use case is as follows;

func closeSessionWithoutFirstProcessingResults(driver *neo4j.Driver) (neo4j.Result, error) {
  if session, err = driver.Session(neo4j.AccessModeRead); err != nil {
    return nil, err
  }
  defer session.Close()

  return session.Run("UNWIND RANGE(1,100) AS N RETURN N", nil)
}

This PR makes session to buffer all pending results into result buffers before closing the underlying connection and makes the results available should they be used. On the contrary, in case of an explicit transaction - the transaction will eventually be rolled back if neither Commit or Rollback is called.

It is important to note that closing sessions before processing executed statement results is not a good practice and should be avoided - it may hide underlying errors which would be visible otherwise.